Those six Superstars are not only six of the greatest in WWE history, they were all top stars during the WrestleMania era. For years, fans waited with bated breath to find out who they would compete against at the biggest show of the year.

Bray Wyatt

The leader of the Wyatt Family is not only the best potential WrestleMania opponent for Cena, he is also the most likely, following the events of Sunday night's Royal Rumble pay-per-view.

Wyatt's interference during the WWE title match between Cena and Orton signified the beginning of a program that will likely play up the bringing down of the machine that Wyatt has repeatedly mentioned in promos dating back to his debut this past July.

Cena is the unquestioned franchise player of World Wrestling Entertainment—the man that sells tickets and merchandise, and the one the company relies on to headline its biggest shows. Sometimes to a fault. But there is no denying that Cena is WWE, through and through.

Who better to start with in an attempt to bring down the so-called "machine?"

Wyatt proved Sunday night at the Royal Rumble that he can hang with top stars and deliver show-stealing matches. His bout with Daniel Bryan was one of the few bright spots of the annual January extravaganza. He showed great explosiveness when the time called for it and his control spots on Bryan, which can turn into lulls in the action for some competitors, never bored the Pittsburgh audience.

That will work to his advantage in a potential WrestleMania match against Cena, who is typically the enemy of the diehard audiences that fill the arenas for the Showcase of the Immortals.

Cena's comeback move set typically incites a chorus of boos from any audience where he performs, thanks to the fact that he has been using it for the majority of his WWE career. So Wyatt's ability to explode with a huge strike will help to create the false hope spots and keep the match unpredictable.

His facial expressions and mannerisms will only help to better tell the story of the bout.

Speaking of story, there are not many more simple stories to tell heading into WrestleMania.

Cena is everything Wyatt hates about the world he lives in. He is the false idol, the hero living in a time of villains, and Wyatt will have the opportunity to exorcise him at the biggest show in sports-entertainment...if the match takes place, as has been hinted at strongly over the last week.

Brock Lesnar

The Beast Incarnate has two losses on his resume since returning to WWE the night after WrestleMania 28, in 2012.

One of them was to Triple H at WrestleMania 29 last April, and he managed to right that wrong the following month at Extreme Rules.

The other? His Extreme Rules match two years ago to John Cena. It is the one blemish he has not had the opportunity to correct.

Their first match was a legitimate Match of the Year candidate that managed to take a Chicago crowd, whose hatred for Cena is well known, and turn them in Cena's favor, thanks to an unholy beating suffered at the hands of the Beast, and a dramatic comeback spot late in the bout.

The blood and violence in that match played a huge role in the lasting effect it had on fans. The sight of a bloodied, beaten Cena managing to come up with one lucky strike before planting Lesnar with the Attitude Adjustment and scoring an improbable win was great booking. Despite the loss, the monstrous Lesnar maintained his aura of invincibility while Cena continued to build upon his legacy.

Thus far, 2014 has seen a meaner, angrier and more focused Lesnar than the one fans were exposed to during his first two years back with WWE. What better way to capitalize on that attitude change than by booking him in the one big rematch the company still has to offer in front of what is sure to be a huge audience in New Orleans on April 6?

With Paul Heyman accompanying Lesnar, he can address the audience and sell the match as Lesnar's one big regret since returning to WWE and really put over the importance a win over Cena has to his client.

Cena, the ultimate hero, can be the Superstar to stand up to the biggest bully on the block.

The likelihood of said rematch may be low, thanks to Lesnar's apparent involvement in the WWE title picture and rumors of a potential match between he and Undertaker, but the biggest stage in wrestling would be fitting for the big rematch.

To even attempt to live up to the original, however, the company would have to waive its "no blood" rule and allow the performers to try to replicate the violent nature of their first bout. If that does not happen, the likelihood of the rematch living up to the lofty standards set by the 2012 match decreases significantly, regardless of when it takes place.

Daniel Bryan

Credit: WWE.com

The SummerSlam main event between Cena and Daniel Bryan this past August, in which Bryan captured his first WWE Championship, was one of 2013's finest matches. To WWE's credit, they have yet to exhaust fans with rematch after rematch of the classic encounter.

That could change come WrestleMania, if WWE wanted it to.

Sure, figuring out a creative way to get there without straining may be difficult, but does it really matter?

Pack New Orleans' Superdome with over 70,000 fans, put the two Superstars with the loudest reactions in all of wrestling in the same ring, and let them do what they do.

Preferably with a title on the line.

And 20-plus minutes to work their magic.

Then sit back and marvel at the fact that two full-time members of the roster can steal the show out from underneath a handful of part-time stars brought back to pop a buyrate.

The Undertaker

Credit: WWE.com

There is one big money match WWE still has in its bag of tricks that it has yet to utilize to this point, and it involves the company's answer to Superman, Cena, attempting to break the legendary undefeated streak of the greatest phenom in company history, The Undertaker.

While they have competed against one another in the past, it has never been on as grand a stage as the one WrestleMania presents.

Cena's character is one that rises to the occasion, overcomes the odds and does things that other Superstars cannot. It would be incredibly easy to throw together a storyline in which he states that the only thing he has not accomplished in his career is ending the most fabled streak in wrestling history.

He states his intention to challenge the streak this year, bringing out Undertaker to accept and setting up one of the biggest, most anticipated matches in WrestleMania history.

Creative could literally wait until the go-home episode of Raw to announce the match and it would still do great pay-per-view buys and would probably result in a large number of WWE Network subscriptions.

Two of the biggest stars in wrestling, including the most polarizing performer of all time, clashing in a main event with so much at stake, is everything a WrestleMania main event should be.

Not to mention the fact that the match would be a great one featuring two Superstars who understand the mat game, and how to tell a story that will keep fans invested.

Why the company has been so hesitant to present Cena vs. Undertaker at 'Mania is absolutely perplexing and only gets significantly more so when one realizes how easy it would be to set up.